1. Field of the Invention
This Invention relates to a method for producing a conductor board and to a conductor board produced thereby.
2. Description of Related Art
It is known that the metalization required to produce conductor paths, connections, etc. may be produced on a ceramic, e.g. an aluminum oxide ceramic, by the so-called “direct bonding technology”, and in the case of copper metalizations, by the so-called “DCB process” (direct copper bonding technology), to wit using metal or copper foils or sheets forming the metalization, that comprise a layer or coating of the metal and a reactive gas, preferably oxygen, on their faces.
In this process, described for example in U.S. Pat. No. 3,711,120 or German Patent 2,319,854, the layer or coating of the chemical compound of the metal and a reactive gas (fusion-applied layer) forms a eutectic having a melting temperature below the melting temperature of the metal (e.g. copper), so that by applying the foil to the ceramic and by heating all layers, these can be joined together, to wit by melting on of the metal, or copper, substantially only in the region of the melt-on or oxide layer.
The DCB process comprises, for example, the following steps:                Oxidizing a copper foil in such manner that a uniform Copper oxide layer results        Placing the copper foil on the ceramic layer        Heating the composition to a processor temperature between about 1065° and 1083° C., e.g. to about 1071° C.        Cooling to room temperature.        
Likewise, a so-called active soldering process, (“diffusion soldering method”) is known for joining metal to carbide ceramics (German Patent 2,213,115). In this known method, an active solder is employed between the metal and the ceramic. The solder has an active metal whose enthalpy of binding to the ceramic is at least 50% of the binding enthalpy of the ceramic in question, so that upon heating to 800–1000° C., not only a joining of the solder to the metalization is achieved, but the active metal contained in the solder also forms binding bridges with the carbide, or ceramic.
There is also a known method of producing a substrate (European Patent 0,627,875) in which, in order to produce a through contacting, i.e. an electrical connection between an upper and a lower metalization within the compass of the substrate, a metal body is placed in an aperture of the insulation layer, and then the body is deformed by pressing, to the thickness of the insulating layer. To complete the through contacting, an electrical connection or bonding is done between the inserted metal body and the metalizations formed by metal foils or coatings. This connection or bonding is done, for example, by the DCB process.
A disadvantage of these known methods is that the bonding takes place at elevated process temperature, and the metal body undergoes a substantially greater thermal expansion than the insulating layer, so that upon bonding, the metalizations lift off the insulating layer at the margin of the particular aperture. Therefore, even after production of the substrate, the metalization in the immediate surroundings of the through contacting are not completely connected to the faces of the insulating or ceramic layer.